1. Field of the Invention
The invention relates to a relative pressure control system and a relative flow control system that control a supplied flow of operating gas to be divided for two systems and to be output at a predetermined division ratio.
2. Description of the Related Art
Conventionally known etching gas supply systems include those of the type that supplies a low-pressure etching gas to a center area and edge area of a wafer. FIG. 29 is a schematic diagram of an overall configuration of a conventional etching gas supply system 300. FIG. 30 is a selectively enlarged cross sectional view of a focus ring 307 shown in FIG. 29.
The conventional etching gas supply system 300 has a vacuum reaction chamber 301 for performing etching. The vacuum reaction chamber 301 has a lower electrode 303 for the use of mounting wafers 302 one by one, and a shower plate 304 is provided thereabove. The shower plate 304 is connected via an operating gas pipeline 306 to flow control valves 305a to 305d. These control valves, respectively, adjust the compositions and flow rates of the operating gases that are supplied from gas sources of, for example, O2, Ar, C4F8, and CO, which are different from one another.
The lower electrode 303 has a focus ring 307 provided in an annular manner such as to surround the outer periphery of the wafer 302. As shown in FIG. 30, the focus ring 307 is formed in the form of a cross-sectional rectangle. A gas flow path 307a abutting the lower electrode 303 is formed concentric with the focus ring 307 on a face contacting the lower electrode 303, and is extended in fluid communication with a plurality of injection ports 307b. As shown in FIG. 29, the gas flow path 307a is connected via an operating gas pipeline 309 to flow control valves 308a to 308d. These control valves, respectively, regulate the flow rates and compositions of operating gases that are supplied from gas sources of, for example, O2, Ar, C4F8, and CHF3, which are different from one another.
The vacuum reaction chamber 301 is provided with an optical system that monitors plasma conditions. An arithmetic processor section 312 inputs an optical signal through an optical divider 311, monitors etching rates, uniformity, and the like of a center area and edge area of the wafer 302, open and close operations of the flow control valves 308a to 308d in accordance with the monitoring results.
Thus, the operating gas is supplied to the center area of the wafer 302 from the shower plate 304. Concurrently, the operating gas is injected onto the edge area of the wafer 302 correspondingly to the process condition of the operating gas from the injection ports 307b of the focus ring 307. Consequently, the wafer 302 can be supplied overall with the operating gas. (see Japanese Unexamined Patent Application Publication No. 2002-217171 (pp. 3 and 4; FIGS. 1 and 2), for example).
(First Problems)
However, in the conventional etching gas supply system 300, the wafer 302 is supplied with the operating gas from the shower plate 304 and the injection ports 307b of the focus ring 307, so that various redundant components are provided. For example, two flowlines, namely, the operating gas pipeline 306 and the operating gas pipeline 309, are provided, and the flow control valves 305a to 305d and 308a to 308d are necessary. In addition, while the control operations of the flow control valves 305a to 305d are being predicted in accordance with the actually processed operating gas on the wafer 302, and the flow rate of the operating gas being injected from the injection ports 307b of the focus ring 307 is controlled. As such, a case can take place wherein the etching gas cannot be uniformly sprayed on the wafer 302.
To overcome the above-described problem, a configuration as shown in FIG. 31 can be contemplated, for example. In this case, a relative pressure control system 310, which controls the etching gas flowing through the operating gas pipeline, is assembled into an etching gas supply system 320. In the configuration, the etching gas is sprayed onto the center area and edge area of a wafer 57 from a center shower 55 and edge shower 56 of an etching shower 54 provided inside a chamber 51. More specifically, solenoid valves 322A and 322B (or, piezoelectric valves, for example) are parallel connected to an operating gas supply valve 53 provided to the operating gas pipeline. In addition, the solenoid valves 322A and 322B are connected to the center shower 55 and edge shower 56 of the etching shower 54 through pressure sensors 323A and 323B. The solenoid valves 322A and 322B, respectively, are controlled by a controller 325 in accordance with detection results obtained by the pressure sensors 323A and 323B. Then, the etching gas flowing through the operating gas pipeline is output at predetermined division ratios, thereby to be sprayed onto the wafer 57 from the center shower 55 and edge shower 56 of the etching shower 54.
However, when the controller 325 enters the state of a runaway, the relative pressure control system 310 is unable to detect the runaway. As such, the operational states of the solenoid valves 322A and 322B (or, piezoelectric valves) that electrically control the open and close operations cannot be recognized. This can probably cause a case wherein although the solenoid valves 322A and 322B are both in fully opened states, the runaway state cannot be recognized. This consequently permits the etching gas to remain in the operating gas pipeline that connects between the operating gas supply valve 53 and the solenoid valves 322A and 322B in, for example, case of emergency, such as the case of a runaway of the controller 325. In such an emergency case, it is demanded that in the etching gas supply system 320, the etching gas be securely drained from the operating gas pipeline. However, a problem remains in that the requirement cannot be satisfied with the solenoid valves 322A and 322B (or, piezoelectric valves, for example) that electrically control on-off valve operations.
(Second Problems)
The method shown in FIG. 31, however, has a problem as described below. Generally speaking, as a method of determining a control objective valve, a method can be contemplated wherein, on the condition that the C/E (center/edge) ratio of a shower plate is 1.000, when the objective pressure ratio is 1.000 or lower, a center-side valve is determined to be a control objective valve. Alternatively, when the objective pressure ratio is greater than 1.000, the edge-side valve is determined to be the control objective valve. However, this method has a problem as described herebelow.
(1) Due, for example, to differences depending on pipeline and/or throttling conditions, to variations of sensor calibration, and to variations in the CV values of the control valves, there occur variations in the actual C/E ratio (which is not limited to 1.000, but is variable to 0.950, 1.080, or the like). This leads to occurrence of a noncontrollable zone (zone between 1.000 and 0.950) corresponding to the variations.
In order to overcome the problem, the configuration may be such that the respective control valve is held standby in a full open mode and is controlled after the flow rate has been stabilized. In this configuration, however, while the noncontrollable zone is not caused, the responsiveness is low, so that requirements for high-speed responsiveness cannot be satisfied. In more specific, in the state after determining the actual pressure ratio to be 0.950, if the control pressure ratio is 0.950 or lower with respect to a pressure ratio C/E of 0.950, then the center-side valve is controlled; and if the control pressure ratio is greater than 0.950, then the edge-side valve is controlled. In this case, no noncontrollable zone is not caused, however, a loss occurs in time necessary to determine the pressure ratio in an inactive state to be 0.950.
(2) In addition, generally, according to a method, the noncontrol-side valve is held in the full open state, and only the other valve is controlled. In the method, when the objective flow rate varies from 200 sccm to 1000 sccm during the partial pressure control, there can occur a noncontrollable event (wherein the flow rate is not converged into the objective value), wherein the event is determined to be abnormal, and valve shift operation is performed. However, the amounts of time used to, for example, determine the abnormality and shift the valve are losses, thereby reducing the responsiveness.
(Third Problems)
An embodiment corresponding to claim 10 for solving the second problem is predicted to have a problem described herebelow.
The control objective valve is determined by determining the threshold value in accordance with the theoretical ratio of the shower plate serving as a device (for example, when the theoretical ratio, is a pressure ratio of 1.000, the threshold value is 1.000.). Consequently, a problem occurs with the method of performing the partial pressure control by determining the control valve in accordance with a predetermined value. The problem is that in the event that the theoretical ratio is not 1:1 but has become, for example, 2:1 or 1:2, the threshold value has to be set in units of the device (in units of the ratio of the shower plate), versatility is impaired, as a problem.
In addition, when the threshold value is mistakenly set, a noncontrollable zone occurs as another problem. More specifically, for example, suppose that whereas the theoretical ratio of the shower plate is 2.000, the threshold value is mistakenly set to 1.000, the objective pressure ratio is set to 1.500. According to such setting, in a practical operation, the center-side valve has to be controlled, however, since the threshold value is set to 1.000, 1.500 is determined to be for the edge-side valve. In this event, the control can be performed within a range of the ratio to 1.918 with the edge-side valve closed 25%. However, 1.500 is smaller than 1.918, so that control shifts to the center-side control, thereby causing a noncontrollable event. Thus, whereas the edge side can be within the range to 1.918, since 1.500 is smaller than 1.918, there occurs the problem of causing the noncontrollable event even with the embodiment corresponding to claim 10.
To solve the first problem, the relative pressure control system according to the present invention comprises the following structures.
(1) A relative pressure control system comprises: a plurality of air operated valves of a normally open type that are connected to an operation gas pipeline supplied with an operation gas; pressure sensors that are series connected to the respective air operated valves and that detect output pressures of the respective air operated valves; a control device that controls operation pressures of the respective air operated valves in accordance with the pressures detected by the pressure sensors; and an interlock mechanism that connects to the control device and that correlates the plurality of air operated valves to one another so that at least one of the plurality of air operated valves is normally opened, wherein an opening of a specified one of the plurality of air operated valves is regulated, and the operation gas is output at a predetermined division ratio.
(2) In the relative pressure control system set forth in (1), the control device performs a comparison between output pressures and specifies one of the plurality of air operated valves as a control objective.
(3) The relative pressure control system set forth in (1), further comprises abnormality detecting means, wherein when the operation gas is supplied by fully opening all the air operated valves, output pressures of the respective air operated valves are detected by the pressure sensors at a fixed interval, and the abnormality detecting means determines whether a pressure ratio of the output pressures exceeds a specified value and detects an abnormality when the pressure ratio exceeds the specified value.
(4) In the relative pressure control system set forth in (1), the control device stores valve models that each determine an operation pressure of a specified one of the air operated valves for the pressure detected by the pressure sensor, and performs feed forward control of the specified one of the air operated valves by using the valve model.
(5) In the relative pressure control system set forth in (4), the control device corrects the operation pressure underwent the feed forward control, by using the pressure detected by the pressure sensor connecting to the air operated valve undergoing the feed forward control.
(6) A relative pressure control system comprises: an operation gas pipeline; proportional control means and fixed orifice means parallel connected to the operation gas pipeline, the proportional control means performing variable control of a flow path area for an operation gas, and the fixed orifice means performing invariable control of the flow path area for the operation gas; pressure sensors that each detects pressures and that are respectively connected to the proportional control means and the fixed orifice means; and a control device that performs proportional control of operation of the proportional control means in accordance with results of detection by the pressure sensors, thereby to perform control of output pressures of the proportional control means and the fixed orifice means.
Further, the relative flow control system according to the present invention comprises the following structures to solve the first problem.
(7) A relative flow control system, comprises: a flow control device including a flow control valve connecting to a gas supply source, and flowrate sensing means for detecting a flowrate being output by the flow control valve, thereby to control the flow control valve in accordance with the results of detection by the flowrate sensing means; the operation gas pipeline connecting to the flow control device; the relative pressure control system including a plurality of air operated valves of a normally open type that are parallel connected to the operation gas pipeline, pressure sensors that are series connected to the respective air operated valves and that detect output pressures of the respective air operated valves, a control device that controls operation pressures of the respective air operated valves in accordance with the pressures detected by the pressure sensors, and an interlock mechanism that connects to the control device and that correlates the plurality of air operated valves to one another so that at least one of the plurality of air operated valves is normally opened, wherein an opening of a specified one of the plurality of air operated valves is regulated, the operation gas is output at a predetermined division ratio; and abnormality detecting means wherein when the operation gas is supplied by fully opening all the air operated valves, output pressures of the respective air operated valves are detected by the pressure sensors at a fixed interval, and the abnormality detecting means determines whether a pressure ratio of the output pressures exceeds a specified value and detects an abnormality when the pressure ratio exceeds the specified value.
(8) In the relative flow control system set forth in (7), the control device stores valve models that each determine an operation pressure of a specified one of the air operated valves for the pressure detected by the pressure sensor, and performs feed forward control of the specified one of the air operated valves by using the valve model.
(9) In the relative flow control system set forth in (8), the control device corrects the operation pressure underwent the feed forward control, by using the pressure detected by the pressure sensor connecting to the air operated valve undergoing the feed forward control.
To solve the second problem, the relative pressure control system according to the present invention comprises the following structures.
(10) A relative pressure control system comprising variable orifice means capable of performing variable control of a plurality of flow path areas in parallel to a single controlled-fluid supply pipeline, pressure sensors respectively series connected to the variable orifice means, and control means that controls open and close operations of the variable orifice means, wherein the controlled fluid is output at a predetermined division ratio from the plurality of variable orifice means, wherein: the control means includes arithmetic sections that calculate respective objective pressures of the plurality of variable orifice means in accordance with the predetermined division ratio and the results of detection of the pressure sensors, and a signal processor section that creates control signals to be supplied to the plurality of variable orifice means in accordance with the objective pressures and that outputs the control signals to all the variable orifice means; and before outputting the signals, the signal processor section outputs fixed-opening signals that each maintain conductance of the plurality of the variable orifice means at a fixed amount.
(11) In the relative pressure control system set forth in (10), preferably, the fixed amount is in a range of from 65% or more to 95% or less of the conductance in a fully opened state.
To solve the third problem, the relative pressure control system according to the present invention comprises the following structures.
(12) A relative pressure control system comprising variable orifice means capable of performing variable control of a plurality of flow path areas in parallel to a single controlled-fluid supply pipeline, pressure sensors respectively series connected to the variable orifice means, and control means that controls open and close operations of the variable orifice means, wherein the controlled fluid is output at a predetermined division ratio from the plurality of variable orifice means, wherein: the control means includes arithmetic sections that normally calculate respective objective pressures of the plurality of variable orifice means in accordance with the predetermined division ratio and the results of detection of the pressure sensors, and a signal processor section that creates control signals to be supplied to the plurality of variable orifice means in accordance with the objective pressures and that normally outputs the control signals to all the variable orifice means.
(13) In the relative pressure control system set forth in (12), when the variable orifice means are of a normally open type, the signal processor section performs a comparison of an amount of operation in accordance with a difference between the objective pressure calculated by the arithmetic section in units of the variable orifice means and an output pressure detected by the pressure sensor; and the signal processor section creates a fixed-opening signal for one of the variable orifice means wherein the amount of operation is a minimum, and creates a control signal necessary for the output pressure to reach the objective pressure for the other variable orifice means.
(14) In the relative pressure control system set forth in (12), when the variable orifice means are of a normally closed type, the signal processor section performs a comparison of an amount of operation in accordance with a difference between the objective pressure calculated by the arithmetic section in units of the variable orifice means and an output pressure detected by the pressure sensor; and the signal processor section creates a fixed-opening signal for one of the variable orifice means wherein the amount of operation is a maximum, and creates, for the other variable orifice means, a control signal necessary for the output pressure to reach the objective pressure.
(15) In the relative pressure control system set forth in (12), preferably, the fixed amount is in a range of from 65% or more to 95% or less of the conductance in a fully opened state.